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1
Content available remote Modelling of the circulation, water exchange and water age properties of the Gulf of Bothnia
100%
Myrberg K. , Andrejev O.
Oceanologia
|
2006
|
tom No. 48 (S)
55-74
EN
To estimate the mean circulation, water exchange and water age in the Gulf of Bothnia a ten-year simulation using a three-dimensional numerical model was carried out. The results confirmed the early findings by Witting (1912) and Palmén (1930) that a mean cyclonic circulation takes place both in the Bothnian Sea and in the Bothnian Bay. However, the modelling results showed clearly that there exist meso-scale circulation features including coastal "jets", not reported in the Witting-Palmén results. The simulated mean currents were also higher than those found earlier, while the persistency of this circulation is typically between 20 and 60%, which is similar to the earlier results. There is a large difference between the various model-based water-exchange estimates: these are strictly dependent on the time-averaging used. Water age proved to reflect properties of the mean circulation system, and the highest water age (of around 7.4 years) was found in the central part of the Bothnian Bay. The water age was found to be rather high also in the entire Gulf of Bothnia, which provides evidence of the rather slow water exchange between the Gulf and the Baltic Sea. This leads to the conclusion that, from the physical point of view, the Gulf of Bothnia is vulnerable to eutrophication.
2
Content available Modelling of the circulation, water exchange and water age properties of the Gulf of Bothnia
100%
Myrberg K. , Andrejev O.
Oceanologia
|
2006
|
tom 48
|
nr S
EN
To estimate the mean circulation, water exchange and water age in the Gulf of Bothnia a ten-year simulation using a three-dimensional numerical model was carried out. The results confirmed the early findings byWitting (1912) and Palm´en (1930) that a mean cyclonic circulation takes place both in the Bothnian Sea and in the Bothnian Bay. However, the modelling results showed clearly that there exist meso-scale circulation features including coastal ‘jets’, not reported in the Witting-Palm´en results. The simulated mean currents were also higher than those found earlier, while the persistency of this circulation is typically between 20 and 60%, which is similar to the earlier results. There is a large difference between the various model-based water-exchange estimates: these are strictly dependent on the time-averaging used. Water age proved to reflect properties of the mean circulation system, and the highest water age (of around 7.4 years) was found in the central part of the Bothnian Bay. The water age was found to be rather high also in the entire Gulf of Bothnia, which provides evidence of the rather slow water exchange between the Gulf and the Baltic Sea. This leads to the conclusion that, from the physical point of view, the Gulf of Bothnia is vulnerable to eutrophication.
3
Content available remote The progress in knowledge of physical oceanography of the Gulf of Finland: a review for 1997-2007
80%
Soomere T. , Myrberg K. , Leppäranta M. , Nekrasov A.
Oceanologia
|
2008
|
tom No. 50 (3)
287-362
EN
The main findings of studies of the physical oceanography of the Gulf of Finland (GoF) during 1997-2007 are reviewed. The aim is to discuss relevant updates published in international peer-reviewed research papers and monographs, bearing in mind that a comprehensive overview of the studies up to the mid-1990s is available (Alenius et al. 1998). We start the discussion with updates on the basic hydrographical and stratification conditions, and progress in the understanding of atmospheric forcing and air-sea interaction. Advances in the knowledge of basin-scale and mesoscale dynamics are summarised next. Progress in circulation and water exchange dynamics has been achieved mostly by means of numerical studies. While the basic properties of circulation patterns in the gulf have been known for a century, new characteristics and tools such as water age, renewal index, and high-resolution simulations have substantially enriched our knowledge of processes in the Gulf of Finland during the last decade. We present the first overview of both status and advances in optical studies in this area. Awareness in this discipline has been significantly improved as a result of in situ measurements. Our understanding of the short- and long-term behaviour of the sea level as well as knowledge of the properties of both naturally and anthropogenically induced surface waves have expanded considerably during these ten years. Developments in understanding the ice conditions of the Gulf of Finland complete the overview, together with a short discussion of the gulf's future, including the response to climate change. Suggestions for future work are outlined.
4
Content available remote A statistical approach to coastal upwelling in the Baltic Sea based on the analysis of satellite data for 1990-2009
80%
Lehmann A. , Myrberg K. , Höflich K.
Oceanologia
|
2012
|
tom No. 54 (3)
369-393
EN
A statistical analysis of Baltic Sea upwelling has been carried out to cover, for the first time, the entire sea area for the period 1990-2009. Weekly composite SST maps based on NOAA/AVHRR satellite data were used to evaluate the location and frequency of upwelling. The results obtained were analysed and compared with earlier studies with excellent agreement. Our study enables the most intense upwelling areas in the entire Baltic Sea to be evaluated. According to the analysis of 443 SST maps, the most common upwelling regions are found off the Swedish south and east coasts (frequency 10-25%), the Swedish coast of the Bothnian Bay (16%), the southern tip of Gotland (up to 15%), and the Finnish coast of the Gulf of Finland (up to 15%). Pronounced upwelling also occurs off the Estonian coast and the Baltic east coast (up to 15%), the Polish coast and the west coast of Rügen (10-15%); otherwise the upwelling frequency was between 5 and 10%. Additionally, simulated SST distributions derived from a Baltic Sea numerical model were analysed for the same period. Furthermore, at specific positions close to the coastline, surface winds based on the SMHI meteorological data base were analysed for the same 20-year period. Wind components parallel to the coast were discriminated into favourable and unfavourable winds forcing upwelling. The obtained frequencies of upwelling-favourable winds fit very well the observed upwelling frequencies derived from satellite SST maps. A positive trend of upwelling frequencies along the Swedish east coast and the Finnish coast of the Gulf of Finland was calculated for the period 1990-2009.
5
Content available The progress in knowledge of physical oceanography of the Gulf of Finland: e review for 1997-2007
80%
Soomere T. , Myrberg K. , Lepparanta M. , Nekrasov A.
Oceanologia
|
2008
|
tom 50
|
nr 3
287-362
EN
The main findings of studies of the physical oceanography of the Gulf of Finland (GoF) during 1997–2007 are reviewed. The aim is to discuss relevant updates published in international peer-reviewed research papers and monographs, bearing in mind that a comprehensive overview of the studies up to the mid-1990s is available (Alenius et al. 1998). We start the discussion with updates on the basic hydrographical and stratification conditions, and progress in the understanding of atmospheric forcing and air-sea interaction. Advances in the knowledge of basinscale and mesoscale dynamics are summarised next. Progress in circulation and water exchange dynamics has been achieved mostly by means of numerical studies. While the basic properties of circulation patterns in the gulf have been known for a century, new characteristics and tools such as water age, renewal index, and high-resolution simulations have substantially enriched our knowledge of processes in the Gulf of Finland during the last decade. We present the first overview of both status and advances in optical studies in this area. Awareness in this discipline has been significantly improved as a result of in situ measurements. Our understanding of the short- and long-term behaviour of the sea level as well as knowledge of the properties of both naturally and anthropogenically induced surface waves have expanded considerably during these ten years. Developments in understanding the ice conditions of the Gulf of Finland complete the overview, together with a short discussion of the gulf’s future, including the response to climate change. Suggestions for future work are outlined.
6
Content available Dynamic features of successive upwelling events in the Baltic Sea - a numerical case study
80%
Myrberg K. , Andrejev O. , Lehmann A.
Oceanologia
|
2010
|
tom 52
|
nr 1
77-99
EN
Coastal upwelling often reveals itself during the thermal stratification season as an abrupt sea surface temperature (SST) drop. Its intensity depends not only on the magnitude of an upwelling-favourable wind impulse but also on the temperature stratification of the water column during the initial stage of the event. When a ‘chain’ of upwelling events is taking place, one event may play a part in forming the initial stratification for the next one; consequently, SST may drop significantly even with a reduced wind impulse. Two upwelling events were simulated on the Polish coast in August 1996 using a three-dimensional, baroclinic prognostic model. The model results proved to be in good agreement with in situ observations and satellite data. Comparison of the simulated upwelling events show that the first one required a wind impulse of 28 000 kg m−1 s−1 to reach its mature, full form, whereas an impulse of only 7500 kg m−1 s−1 was sufficient to bring about a significant drop in SST at the end of the second event. In practical applications like operational modelling, the initial stratification conditions prior to an upwelling event should be described with care in order to be able to simulate the coming event with very good accuracy.
7
Content available remote Dynamic features of successive upwelling events in the Baltic Sea - a numerical case study
80%
Myrberg K. , Andrejev O. , Lehmann A.
Oceanologia
|
2010
|
tom No. 52 (1)
77-99
EN
Coastal upwelling often reveals itself during the thermal stratification season as an abrupt sea surface temperature (SST) drop. Its intensity depends not only on the magnitude of an upwelling-favourable wind impulse but also on the temperature stratification of the water column during the initial stage of the event. When a "chain" of upwelling events is taking place, one event may play a part in forming the initial stratification for the next one; consequently, SST may drop significantly even with a reduced wind impulse. Two upwelling events were simulated on the Polish coast in August 1996 using a three-dimensional, baroclinic prognostic model. The model results proved to be in good agreement with in situ observations and satellite data. Comparison of the simulated upwelling events show that the first one required a wind impulse of 28000 kg m-1 s-1 to reach its mature, full form, whereas an impulse of only 7500 kg m-1 s-1 was sufficient to bring about a significant drop in SST at the end of the second event. In practical applications like operational modelling, the initial stratification conditions prior to an upwelling event should be described with care in order to be able to simulate the coming event with very good accuracy.
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